CE 515 Railroad Engineering

Railway StructuresDesign ConsiderationsSource: AREMA Ch. 8

“Transportation exists to conquer space and time -”

bad powerpoints video!

Loading Design

• ACI , AISC , AASHTO

• AREMA Manual for Railway Engineers

• Different Types of Loadings

Differences From Roadway to Railroad Structures

Versus

Image from http://www.fra.dot.gov/us/content/4

Image from http://images.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/

Life Span

• 100 Year Life Span

• Due to viable of alternative routes

Dead Loads

• Permanently remaining items supported by the structure

• Track is 200lbs/linear ft. • Ballast is 120lbs/ft3

• Treated Timber 60lbs/ft3

What went wrong

Image from : http://www.time.com/time/photogallery/0,29307,1649646_1421688,00.html

Live Loads

• Static and Dynamic effect load of vehicles

• Cooper E-Series loading Scheme (E-1)

Image from: http://www.tpub.com/content/armytransportation/TI-850-02/TI-850-020112.htm

Cooper E-Series

• Conversions for modern to E-series • Bridge Specific Rating System• Bridges Rated off Limiting Structure• Service Rating vs. Ultimate Rating

Live Load 4-Axel

• Short Span Steel Members (<54ft)

• Heavy Intermodal Trains

• More Similar Loading to 4-axle coupled cars

Impact Loading

• Dynamic increment and impulsive loads

• Caused mostly by flat wheel spots

• Designer has no control over imposition

• Load amount derived from percent of live load

Flat Wheel on Engine

Steel Concrete and Timber Structures Impact Loading

• Steel impact load is function of spacing of supporting elements

• Differences for prestressed than cast-in-place concrete impact loading calculations

• Not taken into account for timber due to material properties and AWS design

Centrifugal Force

• Outward acting force on curve from train• Force bend structure laterally• Steel structure loads laterals and cross frames• Concrete Structures usually stiff enough to

resist• Track super elevation offers some

compensation

Lateral Loads

• Nosing, hunting action, lurching and damaged rolling stock

• Train Hunting

• Due to routine train passage

Sssshhh. Be vewy vewy quite. I’m hunting twains.

http://www.flickr.com/photos/leadegroot/2311723124/

Longitudinal Loads

• Braking and Accelerating Force

• Distributed into the supporting structure

Wind and Stream/Ice/Buoyancy Loads

• Wind loading self explanatory wind force on structure and train

• Stream loads are loaded in every way horizontal, vertical, and buoyancy

• Vessel collision also a factor

In Russia

http://englishrussia.com/?m=200612&paged=5

Seismic Loads

• Induce horizontal and vertical design

• Track works as a damping agent

• Three defined levels of ground motion

Fatigue

• What most railroad are designed for!

• From repetitive stress loadings causing cracks

• Often limit designer to bolted connection

Fracture Critical Member (FCM)

• Any member where failure result in ultimate bridge failure

• FCM are held to higher design criteria

Deflection, Corrosion and Bearing/Volumetric Changes

• Deflection control when long span and high strength materials used

• Use of weathering steel popular• Bearing transfer all load from superstructure

to substructure while still allowing rotation and translation

• Thermal Changes

Weathering Steel Bridge

Retaining Wall Loads

• Contain within the right of way

• 100 year life cycle

• Live loading envelope of track structure